Molecular tools for understanding distribution and spread of weed genotypes

There is increasing interest in documenting and understanding the spread of weed genes or genotypes in cropping systems. In part, this is driven by concern about the ecological consequences from the introduction of genetically engineered crop varieties. Despite this, applications such as managing the spread of herbicide resistant weeds or understanding the importance of immigration of new genes to the awakening of sleeper weeds are probably more important issues. There are a variety of molecular tools that can be applied to these problems. However, it is important to understand the strengths and weaknesses of these tools and the pollination biology of the target species before choosing an approach. For example, molecular markers that are unassociated with the gene of interest may be useful with species that are mostly self-pollinated, but are generally impractical for tracking gene movement in species with significant levels of outcrossing. This paper will discuss the application of molecular and other tools to the movement of herbicide resistance genes within and between populations. The application of different molecular tools, in combination with other techniques to the problem will be illustrated.